The long-term objective is to elucidate the mechanisms which give rise to endothelial cell heterogeneity. Different endothelia (e.g. myocordial capillary endothelia vs. lung capillary endothelia) have been shown to possess different cell surface antigens. An hypothesis has been proposed which states that the endothelia of new vascular ingrowth becomes specialized in response to the unique characteristics of the surrounding epithelium. This proposal is designed to allow preliminary examination of that hypothesis and form the basis for subsequent more detailed investigations. Advantage will be taken of the presence of a capillary endothelial cell surface glycoprotein (PAS IV) which, in bovine tissues, is present in some epithelial tissues (eg. heart, liver, and mammary gland) but not others (eg. lung and brain). A similar if not identical glycoprotein is present in human tissues. PAS IV will be purified from human tissue and antibodies specific for human PAS IV will be produced and characterized. Evidence will be sought for host tissue control of PAS IV expression through immunofluorescent localization and antigen characterization studies. Endothelial cell surface heterogeneity is undoubtedly a product of tissue - specific endothelial cell function. Knowledge of the basis for the surface antigen heterogeneity will aid our understanding of endothelial cell function. These studies are of general biological significance and may assist in our understanding of cell-cell and cell-matrix interactions between other cell types.